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    <title>Document</title>
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<body>
    <div id="q1"><span>第一个js</span></div>
    <input type="button" id="q2" value="点击修改"> 
    <script>
        $("#q2").click(function () {
            $("#q1").text("修改后的js");
        })
    </script>   
</body>
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